Retaining walls cure variety of woes
The Tulsa, Okla., State Highway Commissioner had a vested interest in the 44th Avenue West street-widening project. Because he regularly drove the route, he took a personal interest in making sure the project was done right.
The project involved a 34-foot-wide cut to accommodate a proposed 26-foot-wide road, as well as curbs, gutters and sidewalks. But a 12-foot-high earth berm helped deaden traffic noise for residents living near the road. Improvements would have left a 1:1 slope on the berm down to the designed street profile grade.
Traditionally, a poured-in-place concrete retaining wall would have been designed to provide hillside erosion control. However, Mike Case, commissioner of OKDOT’s District 8, requested that a segmental unit retaining wall be considered as a viable alternative.
The city’s engineering department agreed, ultimately opting for a soil reinforced Versa-Lok retaining wall system.
The application of Segmental Retaining Walls (SRWs), using manufactured concrete units, is a new technology applied to the age-old concept of soil retainment. Soil-reinforced retaining walls made with natural stone faces have been in use for thousands of years, and when soil reinforcement behind ancient walls was needed, basic but effective woven reed mats were used to reinforce the wall units and soil, allowing them to resist retained soil loads.
Nowadays, a mortarless, comparatively lightweight, dry-stacked SRW is providing simple, low-cost (typically 25 percent to 40 percent less than traditional cast-inplace retaining walls) solutions to a variety of municipal and governmental site and soil retainment problems.
In Tulsa, a series of four- and five-foot-high tiered retaining walls on both sides of the street solved the grade change problem on the street-widening project. It took just 38 days to complete.
Case calls the SRWs “a beautiful solution,” adding that the texture of the walls makes them more difficult for graffiti artists, who like large expanses of smooth concrete, to deface.
But, while Tulsa’s first venture into SRW was a hit, Minneapolis has been using them for several years to solve grade change and erosion problems when reconstruction of city streets affected private property. There, in many cases, property owners were able to maintain full use of their land by the addition of city-installed retaining walls along property lines affected by the construction.
Minneapolis has also used SRWs extensively to replace traditional retaining walls, such as concrete and timber walls, that have failed. Designed for quick installation, they can be hand placed by a single worker without the need for heavy equipment.
And, in Loveland, Colo., SRWs provided an unusual, but highly effective answer to a nagging traffic problem. City engineers were well aware of residents’ complaints about vehicle curb-jumping on a curved section of 37th Street, especially in the winter when the road was icy. Children playing in their own yards were at risk, as was nearby property.
To solve the problem, the city built safety barrier walls using SRWs along 1,2000 lineal feet of the tricky S-shaped section of road.
The 28-inch-high dry-stacked walls were backfilled with soil and native evergreen plantings. The barrier walls have since passed numerous tests, with single-vehicle spin outs and multiple-vehicle accidents confined to the street. Because the walls give on impact, they prevent deflection of vehicles back into oncoming traffic, and they are reuseable.
Additionally, unskilled city crews can easily reinstall the wall with minimal loss of SRW materials and without any demolition, new form work or time consuming redesign and bidding, and residents are impressed with the attractiveness and safety of the walls.